Labor care providers typically aim to admit a laboring woman to the labor unit at the onset of "active" labor, i.e., when the rate of cervical dilation is anticipated to increase. However, active labor can only be determined retrospectively based on changes in dilatation over time. Reports indicate that approximately one-half of regularly contracting, low-risk, nulliparous women are admitted for labor prior to active labor. These women are more prone to intervention during labor including a more than two-fold risk of cesarean delivery compared to women admitted in active labor. These data suggest that additional criteria are needed to more accurately determine labor state prior to admission. Evidence increasingly suggests that labor onset and progression is mediated by inflammatory events and inflammatory biomarkers become increasingly detectable in reproductive tissues and maternal blood as labor advances. The purpose of this study is to determine if inflammatory biomarkers may assist in predicting active labor onset. It is hypothesized that increases in specific inflammatory biomarkers over time can predict an actively dilating state (>0.5 cm/hr, on average, over the first 4 hrs after labor admission) among low-risk, nulliparous women admitted for spontaneous labor onset (n = 200). A descriptive, comparative design will be used to evaluate the association between rates of change in specific inflammatory biomarkers [i.e., white blood cell (WBC) count, serum pro-inflammatory cytokines (IL-12, IL-6, IL-8, TNF-1), C-reactive protein (CRP);and body temperature] over time and the amount of cervical dilation during the first 4 hrs post-admission. Inflammatory biomarkers will be measured at labor admission and again 2 hrs and 4 hrs later. Specific inflammatory biomarker changes over time that will be evaluated include admission ->admission+2hrs, admission ->admission+4hrs, and admission ->admission+2hrs ->admission+4hrs. The magnitude of change in individual inflammatory biomarkers between data collection time points will be used to construct ROC curves with respect to the prediction of active labor. Logistic regression analyses, based on the magnitude of biomarker change, will be performed with classification of labor as the dependent variable, i.e., actively or not actively dilating. Cervical dilatation at admission and several common labor interventions will be included as model covariates. Models running multiple inflammatory biomarkers simultaneously will also be considered. If acute changes in inflammatory biomarkers over time are associated with active labor onset, these biomarkers could be used when making decisions regarding "when" to admit laboring women to the labor room. Maximizing the number of women admitted in active labor is an important step toward improving labor outcomes. Findings from this study will be used to inform the development of a physiology-based labor assessment protocol aimed at maximizing the number of women admitted at or after the onset of active labor. Subsequent studies will also determine the effects that clinical interventions have on labor-associated inflammatory mediators. PUBLIC HEALTH RELEVANCE: Inflammatory events are implicated in initiating labor and propagating its progression. The measurement of inflammatory biomarkers may, therefore, be predictive of active labor onset which, at present, can only be determined retrospectively - often hours after a decision to admit for labor has already been made. Approximately one-half of regularly contracting, low-risk, nulliparous women are admitted for labor prior to active labor and women in this high-volume group are more prone to intervention during labor including a more than two-fold risk of cesarean delivery compared to women admitted in active labor. If acute changes in inflammatory biomarkers over time validly predict active labor onset, their measurement can be used to maximize the number of women admitted in active labor. More positive short- and long-term labor outcomes should follow.